Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets, Net (Excluding Goodwill)		$ 1,706	$ 1,131	$ 1,657	$ 1,325
Amortization	[1]	(16)	(6)
Origination of Mortgage Servicing Rights (MSRs)		262	198
Servicing Assets at Fair Value, Purchased			104
Due to changes in inputs or assumptions	[2]	(27)	(328)
Servicing Asset at Fair Value, Other Changes in Fair Value	[3]	(168)	(160)
Servicing Asset at Fair Value, Disposals		(1)	(2)
Finite-Lived Intangible Assets, Purchase Accounting Adjustments	[4]	(1)
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount		1,628	1,119	1,572	1,307
Amortization	[1]	0	0
Origination of Mortgage Servicing Rights (MSRs)		252	198
Servicing Assets at Fair Value, Purchased			104
Due to changes in inputs or assumptions	[2]	(27)	(328)
Servicing Asset at Fair Value, Other Changes in Fair Value	[3]	(168)	(160)
Servicing Asset at Fair Value, Disposals		(1)	(2)
Servicing Asset at Fair Value, Other Changes that Affect Balance		0
Other Intangible Assets [Member]
Intangible Assets, Net (Excluding Goodwill)		78	12	85	$ 18
Amortization	[1]	(16)	(6)
Origination of Mortgage Servicing Rights (MSRs)		10	0
Servicing Assets at Fair Value, Purchased			0
Due to changes in inputs or assumptions	[2]	0	0
Servicing Asset at Fair Value, Other Changes in Fair Value	[3]	0	0
Servicing Asset at Fair Value, Disposals		0	$ 0
Finite-Lived Intangible Assets, Purchase Accounting Adjustments	[4]	(1)
Commercial Mortgage Servicing Rights [Member]
Servicing Asset at Fair Value, Amount		$ 69		$ 62

[1] Does not include expense associated with non-qualified community development investments. See Note 8, "Certain Transfers of Financial Assets and Variable Interest Entities," for additional information.

[2] Primarily reflects changes in option adjusted spreads and prepayment speed assumptions, due to changes in interest rates.

[3] Represents changes due to the collection of expected cash flows, net of accretion due to the passage of time.

[4] Represents the first quarter of 2017 measurement period adjustment on other intangible assets acquired previously in the Pillar acquisition.